Cable television setback decoder automatic control

ABSTRACT

A setback decoder monitors the IF output from a cable-ready receiver and automatically provides a descrambled audio/video signal back to the receiver for output to the subscriber. When the receiver is tuned to a CATV channel which provides signals in a scrambled format, the decoder detects the scrambled signal, determines whether the subscriber is authorized to view the selected program, and descrambles the signal to provide a descrambled output signal to the receiver. The receiver detects the audio/visual output from the decoder and automatically outputs the audio/visual information to the subscriber.

REFERENCE TO OTHER APPLICATIONS

This is a continuation of application Ser. No. 09/192,631, filed Nov.16, 1998; which is a continuation of application Ser. No. 08/914,968,filed Aug. 20, 1997; which is now U.S. Pat. No. 5,862,219, issued onJan. 19, 1999; which is a continuation of application Ser. No.08/440,201, filed May 12, 1995 (now abandoned).

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates generally to cable television receivers. Morespecifically, it pertains to a setback decoder which automaticallydetects when a scrambled signal is input to a receiver and provides adescrambled output signal to the receiver without requiring any controlmessages between the decoder and the receiver.

2. Description of Related Art

A typical CATV subscriber installation includes a settop descramblerwhich is connected between the CATV service provider and thesubscriber's television or video cassette recorder (VCR). Thedescrambler includes a tuner, for tuning the descrambler to a selectedCATV channel, and a descrambling module, for providing descrambling ofscrambled premium channels that the subscriber is authorized to view. Adescrambled video signal is output from the descrambler to thetelevision or VCR on a predetermined carrier frequency, typicallycorresponding to television channels 3 or 4.

Since the descrambler typically provides a single channel output to thetelevision, many of the built-in functions of the television may becomeinoperative. For example, the “picture-in-picture” feature requires dualtuners for simultaneous receipt of video signals on two televisionchannels. Since descramblers provide only a single output, the“picture-in-picture” feature becomes inoperative. Additionally,subscribers are often frustrated by the need for multiple remotecontrollers, one for controlling the descrambler, a second forcontrolling the television set, and possibly a third for the VCR.

To eliminate the need for a separate tuner within the descrambler,manufacturers have offered televisions with broadband tuners which arecapable of accessing the entire CATV frequency spectrum. However, thesetelevisions do not include descrambling capabilities.

Most recently, cable-ready receivers are being developed which receive aradio frequency (RF) CATV input signal and provide an intermediatefrequency (IF) output to an associated descrambler. These receiversrequire the use of a complicated protocol and signaling arrangementbetween the receiver and the descrambler in order to effectively detectand descramble scrambled CATV input signals viewing by a subscriber.Although the control signaling between the receiver and the descramblerprovides full functionality of the receiver while descrambling thedesired CATV premium channel, this complex arrangement is costly anddifficult to manufacture.

Accordingly, there exists a need for a simple receiver and descramblerarrangement which provides descrambling of scrambled CATV input signals.

SUMMARY OF THE INVENTION

The present invention comprises a setback decoder which monitors the IFoutput from a cable-ready receiver, such as a television or VCR, andprovides a descrambled audio and video (A/V) signal back to thereceiver. When the received CATV signal is scrambled, the decoderautomatically detects the scrambled signal, determines whether thesubscriber is authorized to view the selected program, and descramblesthe signal to provide descrambled A/V output to the receiver. Thereceiver detects the video output signal from the decoder and outputsthe information to the subscriber. Since the decoder automaticallydetects the presence of a scrambled CATV signal and the receiverautomatically detects the input of a descrambled output signal from thedecoder, no control messages are exchanged between the receiver and thedecoder.

Accordingly, it is an object of the present invention to provide asetback decoder for automatically detecting and descrambling scrambledCATV signals and providing a descrambled output.

Other objects and advantages of the system will become apparent to thoseskilled in the art after reading the detailed description of a presentlypreferred embodiment.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a CATV subscriber installation made in accordance with theteachings of the present invention;

FIG. 2 is a block diagram of cable-ready receivers which areindividually coupled to the decoder of the present invention;

FIG. 3 is a block diagram of a cable-ready receiver and a decoder madein accordance with the teachings of the present invention;

FIG. 4 is a flow diagram of the process used by the processor within thedecoder;

FIG. 5 is a schematic diagram of the audio switching module in thereceiver of FIG. 3;

FIG. 6 is a schematic diagram of an alternative embodiment of the audioswitching module of FIG. 5;

FIG. 7 is a block diagram of the AGC module in the receiver of FIG. 3;

FIG. 8 is a schematic diagram of the video switching module in thereceiver of FIG. 3;

FIG. 9 is a schematic diagram of the video output section used in thedecoder of FIG. 3;

FIG. 10 is the audio output section used in the decoder of FIG. 3;

FIG. 11 is a block diagram of a first alternative embodiment of thedecoder of FIG. 3;

FIG. 12 is a block diagram of a first alternative embodiment of thereceiver of FIG. 3; and

FIG. 13 is a block diagram of an alternative embodiment of the presentinvention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The preferred embodiment of the present invention is shown in FIG. 1.The CATV subscriber installation 10 includes one or more cable-readyreceivers, which are shown in FIG. 1 as a television 12 and a VCR 14.The receivers 12, 14 are connected to a CATV input 16 and a splitter 17to receive programming signals from the CATV provider. The input line 16is connected to a conventional fiber-coax CATV network. Alternatively,the input line 16 may be connected to a microwave antenna to receive“wireless cable” programming. A received CATV signal comprises a carriersignal and A/V information. Each receiver includes a frequency agilebroadband tuner 36 (shown in FIG. 3), which is selectively tuned tospecific CATV channels. The output from the tuner 36 is externallyaccessible on an intermediate frequency (IF) carrier.

As shown in FIG. 2, each receiver 12, 14 is individually connected to adecoder 18, which automatically detects when a scrambled CATV signal isreceived by the receiver 12, 14 and provides a descrambled A/V signal tothe receiver 12, 14, as will be described in detail hereafter. Thereceivers 12, 14 are controlled by the subscriber via an IR remotecontrol 20, for selection of a desired CATV channel.

The preferred embodiment of the present invention will be described withreference to FIG. 3. The CATV receiver is shown in FIG. 3 as atelevision 12. However, the receiver may comprise a VCR 14 or any othertype of cable-ready device which accepts a broadband RF input signal andoutputs the received A/V information on an IF carrier. The television 12is coupled to the CATV network via a coaxial cable 32 terminated with anF-type connector 34 at a CATV input port 31. The CATV operator providesbroadcast and interactive video and audio programming on a plurality of6 MHz channels to the subscriber over the full bandwidth of the CATVnetwork, which may be up to 1 Ghz.

A tuner 36, coupled to the CATV port 31, tunes to the specific carrierfrequency of the channel selected by the subscriber. The tuner 36removes the carrier frequency and amplifies the resulting A/V signal.The gain of amplifier is controlled so that the output of the tuner 36remains essentially constant despite variations in strength of the CATVinput signal. When a “normal” or unscrambled CATV signal is received bythe tuner 36, the amplifier is controlled by the television signalprocessing circuitry 40. However, as will be explained in detailhereinafter, when a scrambled CATV signal is received, the decodermodule 18 will control the gain of the amplifier through the AGC module39.

The received A/V signal is output from the tuner 36 on an IF carrier toa signal splitter 38. If no descrambling is required, the A/V signal isprocessed by the signal processing circuitry 40. Audio and videoinformation is separated and processed by the signal processingcircuitry 40 to provide video output to a monitor 44 and audio output tospeakers 46. A subscriber, therefore, will be able to view and listen tothe selected program. A detailed discussion of the signal processingcircuitry 40, which is well known to those skilled in the art, isoutside the scope of this description.

When scrambled CATV input signals are received by the tuner 36, such ason premium cable television channels, interactive video channels, andpay-per-view channels, the signal processing circuitry 40 will be unableto descramble and process the A/V signal. Therefore, the audio and videoprograms will be unintelligible. To descramble the A/V signal, the A/Vsignal is forwarded on a selected IF carrier, preferably 45 MHz, throughthe signal splitter 38 to an IF/AGC port 42 for use by an externaldevice.

The decoder 18 includes a tuner 53 which is selectively tuned to the IFcarrier output from the television 12. The IF/AGC port 52 on decoder 18and the IF/AGC port 42 on television 12 are connected via a coaxialcable 41, terminated at both ends by F-type connectors 49, 51.

A processor 55 within the decoder 18 receives and processes the A/Vsignal using several software-implemented modules, as shown in FIG. 4.The scramble detection module 54 continually monitors the received A/Vsignal (step 100). If the scramble detection module 54 detects that thesignal is not scrambled (step 102), the processor 55 takes no furtheractions and no signals are output from the decoder 18. There are manytypes of audio and video scrambling, scrambling detection, anddescrambling techniques that are well known by those skilled in the art.A detailed discussion of these techniques is outside the scope of thisinvention. If the scramble detection module 54 determines that thesignal is scrambled (step 102), the module 54 determines whether thetype of scrambling being utilized may be descrambled by the descramblingmodule 58 (step 104). If the scrambling technique is not supported (i.e.cannot be descrambled) by the descrambling module 58, the decoder 18takes no further action.

If the technique used to scramble the A/V signal is a compatiblescrambling technique, the authorization module 56 determines whether thesubscriber is authorized to receive the scrambled video services thathave been selected (step 106). As is well known to those skilled in theart, authorization information, such as a subscriber address identifier,is detected on the specific channel being monitored by the decoder 18.This information is compared to an authorization code stored within thememory of the processor 55 to determine if the subscriber is anauthorized user.

Alternatively, the CATV scrambling system may use extra RF carriers(out-of-band) to send address, control and authorization data to theaccess control device. As shown in FIG. 11, the CATV input may “loopthrough” the decoder 18 prior to entering the television 12. Thispermits access by the decoder 18 to the extra RF carriers.

If the subscriber is not authorized, the decoder 18 provides a videooutput signal to the video port 83 (step 112) to inform the subscriberthat they have not been authorized to receive the selected service. Thismessage may also include instructions to enable the subscriber to orderand pay for the service to become an authorized user. These types ofmessages are commonly used for pay-per-view video services.

Once the authorization module 56 determines that the subscriber isauthorized to receive the service, the A/V signal is descrambled (step108 ) by the descrambler module 58. An input/output (I/O) module 59within the decoder 18 provides a low impedance DC signal to the AGCmodule 39 through the IF/AGC port 52. As shown in FIG. 7, the lowimpedance signal from the decoder 18 is input to the tuner 36 andoverrides the higher impedance AGC signal from the signal processingcircuitry 40. This permits the decoder 18 to automatically control thegain of the tuner's amplifier when a scrambled signal is detected by thedecoder 18. No control messages between the television 12 and thedecoder 18 are required.

The descrambled baseband A/V signals are output from the input/output(I/O) module 59 to the input detection and switching module 64 via theA/V output ports 83, 84, 85 the shielded cable 90 and the A/V inputports 80, 81, 82. When the detection and switching module 64 detects asignal at the input ports 80, 81, 82, it switches the source of the A/Vinput provided to the signal processing circuitry 40 from the tuner 36to the decoder 18. Accordingly, the signal processing circuitry 40 willdisplay descrambled A/V output to the monitor 44 and the speakers 46.

A more detailed explanation of the I/O module 59 will be presented withreference to FIGS. 9 and 10. The audio and video signals are separatelydescrambled and output.

The video output section 91 is shown in FIG. 9. The IF carrier with theA/V information is received through port 52. When the scramble detectormodule 54 detects a scrambled signal, a pulse train is output from theauthorization module 56 which provides the descrambling synchronization.Diode D2 turns on transistor Q6 through current limiting resistor R9when the drive pulses are at 0 VDC. Resistor R10 allows transistor Q6 toturn off when current is no longer applied to the base of transistor Q6.When transistor Q6 is turned-on, current flows across theemitter-collector junction of transistor Q 6 through current limitingresistor R11 charging capacitor C3. Capacitor C3 stores energy andensures that transistor Q7 turns on while the pulses are present.

Transistor Q7 acts as a current sink thereby turning on relay K2.Resistor R12 dissipates the energy across capacitor C3 when the drivepulse is no longer present. Relay K2 closes a pair of normally opencontacts which complete the circuit to output a low impedance AGC outputsignal from the decoder 18 to the external AGC/IF output 52. Thedescrambled video signals from the processor 55 flow through capacitorsC4 and C5 to the output connector 83. When the decoder 18 detects ascrambled signal, and relay K2 is energized, the AGC signal is outputfrom the decoder 18 through operational amplifier IC1 and throughcurrent limiting resistor R17 and inductor L1. Resistors R14, R15 andR16 provide the feedback around the operational amplifier and variablegain.

In the same manner, as shown in FIG. 10, descrambled audio signals aredescrambled and output from the audio output section 93.

The detection and switching module 64 included within the television 12will be explained in greater detail with reference to in FIGS. 5, 6 and8. As shown in FIG. 5, a descrambled audio signal from the decoder 18 ispresented to the audio input ports (left and right) 81, 82. In thepreferred embodiment, an audio switch 65 is provided for each audiochannel (left and right). The audio switching module 65 providesswitching from “normal” unscrambled audio signals from the tuner 36 todescrambled audio signals from the decoder 18 using relay K1 andtransistor Q1. The audio signals from the decoder 18 have a DC componentwhich is blocked by capacitor C1. Capacitor C1 allows the audio portionof the signal to be amplified. The DC component of the signal flowsthrough current limiting resistor R1 to the base of transistor Q1. Aresistor R2 is connected from an available 12 VDC supply from the signalprocessing circuitry 40 to the base of transistor Q1. This resistor R2allows transistor Q1 to turn off when current is no longer applied tothe base of transistor Q1. The emitter of transistor Q1 is alsoconnected to the 12 VDC supply. The DC component from the decoder 18turns transistor Q1 on. Current flows from the 12 VDC supply through theemitter-collector junction of transistor Q1 to relay coil K1.

Associated with relay K1 is a set of form C contacts. When relay coil K1is energized, the contacts switch from the normal audio signals receivedfrom the tuner 36 to the descrambled audio signals provided by setbackdecoder 18. Suppression diode D1 protects transistor Q1 from the reverseinductive surge from relay coil K1 upon de-energization.

An alternative embodiment of the audio switching module 65, using CMOSsemiconductor switches, is shown in FIG. 6. Each semiconductor switchQ4, Q5 has an input, an output and a control gate. When voltage isapplied to the control gate, the switch conducts. Capacitor C2 blocksthe DC portion of the decoder 18 audio signal from entering the audioamplifier within the signal 10 processing circuitry 40. CMOS switch Q5is controlled by transistor Q3 and CMOS switch Q4 is controlled bytransistor Q2. When no input is detected from the decoder 18, CMOSswitch Q5 is held in a state of conduction by current flowing throughcurrent limiting resistor R8. When a descrambled audio signal isdetected, the DC component on the audio signal flows through currentlimiting resistor R3, turning-on transistor Q2. Resistor R4 allowstransistor Q2 to turn off when current is no longer applied to the baseof transistor Q2. When transistor Q2 is turned on, current flows acrossthe emitter-collector junction and through current limiting resistor R6,turning-on transistor Q3. When transistor Q3 is turned-on, current flowsthrough resistor R8 through the collector-emitter junction to signalcommon, thereby acting as a current sink.

When transistor Q3 is turned on, the collector of transistor Q2 is lesspositive than when transistor Q2 is turned-off, thereby turning off CMOSswitch Q5. In conjunction with turning transistor Q3 on, current alsoflows through transistor Q2 thereby turning CMOS switch Q4 on.Transistors Q2 and Q3 provide a complimentary switching action for CMOSswitches Q4 and Q5.

Resistor R7 provides a ground path from the base of transistor Q3 tosignal common allowing transistor Q3 to turn-off when current is nolonger applied to the base of transistor Q3 by transistor Q3 when thedescrambled audio signal is no longer present.

Referring to FIG. 8, a video switching module 69 for switching between“normal”, or unscrambled video signals, received from the tuner 36 anddescrambled video signals from the decoder 18 is shown on FIG. 8. Whenno signal is present at the input 80 to the module 69, transistor Q8 andrelay K3 are turned off, thereby allowing the normal video signal fromthe tuner 36 to pass through to the signal processing circuitry 40. Whena descrambled signal is present at the input 80 to the module 69, the DCcomponent on the signal is blocked by capacitor C7 and is passed to thebase of transistor Q8 through current limiting resistor R18. ResistorR19 allows transistor Q8 to turn off when current is no longer appliedto the base of Q8. When transistor Q8 is turned on, current flows acrossthe emitter-collector junction of transistor Q8 and energizes relay K3.The associated form C contacts of relay K3 switches the video input tothe signal processing circuitry 40 from the tuner 36 to the signaloutput by the decoder 18. Suppression diode D6 protects transistor Q8when the descrambled drive pulse terminates which turns-off transistorQ8.

The component values of FIGS. 5-10 are listed below in Table 1.

TABLE 1 COMPONENT FIGURE NO. SPECIFICATION C1 5 330 μF C2 6 33 0 μF C3 910.0 μF C4 9 330 μF C5 9 330 μF C6 9 .001, non polarized C7 8 330 μF C97 .001 μF C11 10 330 μF D1 5 1N4148 D2 9 1N4148 D3 9 1N4148 D6 8 1N4148IC1 9 741 op amp K1 5 Radio Shack 275-241 K2 9 Radio Shack 275-241 K3 8Radio Shack 275-241 L1 9 2.2 μH L2 7 2.2 μH Q1 5 2N3906 Q2 6 2N3906 Q3 62N3904 Q4 6 CD4016 Q5 6 CD4016 Q6 9 2N3906 Q7 9 2N3904 Q8 8 2N3906 Q1010 2N3904 R1 5 1.0 kΩ R2 5 3.3 kΩ R3 6 1.0 kΩ R4 6 3.3 kΩ R5 6 3.3 kΩ R66 10.0 kΩ R7 6 3.3 kΩ R8 6 4.7 kΩ R9 9 1.0 kΩ R10 9 3.3 kΩ R11 9 1.0 kΩR12 9 10.0 kΩ R13 9 1.0 kΩ R14 9 10.0 kΩ R15 9 2.0 kΩ R16 9 2.2 kΩ R17 91.5 kΩ R18 8 10 kΩ R19 8 3.3 kΩ R20 8 75 Ω R23 10 3.3 kΩ R24 10 3.3 KΩR25 10 1 KΩ

Since the decoder 18 automatically detects the presence of a scrambledCATV signal and the television 12 automatically detects the presence ofa descrambled output signal from the decoder 18, no control messages areexchanged between the television 12 and the decoder 18.

The preferred embodiment will operate when analog scrambled signals aredetected on the 6 MHz CATV channel. However, digital CATV systemsmultiplex a plurality of video and audio signals onto a single CATVchannel. Accordingly, the television 12 must inform the decoder 18 whichsub-channel of the digital multiplex to select. As shown in FIG. 12, thetelevision signal processing circuitry 40 outputs a four to twelve bitsub-channel designation, or word, at a frequency above DC and below theIF carrier output to the decoder 18. A four bit word is required for upto 16 sub-carriers, and a twelve bit word is required if a true channeldesignator is desired. Preferably, the sub-channel number is output fromthe signal processing circuitry 40 on a 38 KHz carrier to a multiplexer141. The decoder 18 detects the 38 KHz signal multiplexed with the IFcarrier and forwards the sub-channel designation to the descramblingmodule 58 to descramble the desired sub-channel.

Those skilled in the art -would appreciate that multiple decoders 18 maybe connected in parallel via the IF/AGC port 42 by using a unity-gainsignal splitter with a DC bypass. As described above, only a decoder 18capable of descrambling the received signal will attempt to do so. Thedecoder will place a DC signal on the IF/AGC 41 line to control thetuner 36 amplifier gain. Descrambled A/V signals will be output to theappropriate ports 80, 81, 82 for detection by the input detection module64.

Although the invention has been described in part by making detailedreference to the preferred embodiment, such detail is intended to beinstructive rather than restrictive. For example, although the preferredembodiment of the decoder 18 is shown as a stand alone module, thedecoder 18 may be incorporated as a module within the receiver, as shownin FIG. 13. It will be appreciated by those skilled in the art that manyvariations may be made in the structure and mode of the operationwithout departing the spirit and scope of the invention as disclosed inthe teachings herein.

I claim:
 1. A decoder, for detecting and descrambling scrambled CATVchannel signals, for use in conjunction with a cable-ready receiverwhich receives a multichannel signal; wherein the cable-ready receiverincludes a frequency agile tuner which receives said multichannel signaland outputs a selected CATV channel signal, the tuner output coupled toa video display and speaker unit; a receiver output port coupled to saidtuner output for outputting the selected CATV signal; and an overrideinput port for receiving a descrambled CATV channel signal from thedecoder and for overriding the selected CATV signal output by the tunerto the video display and speaker unit when a descrambled signal isreceived at the override input port; the decoder comprising: means forreceiving a CATV channel signal output by the receiver output port;means for detecting whether said received CATV channel signal isscrambled and means for automatically turning on or off descramblingmeans for descrambling said received CATV channel signal; descramblingmeans for descrambling a scrambled CATV channel signal; decoder outputport means for outputting a descrambled CATV channel signal; and decoderoutput control means for controlling the output of said decoder outputport means such that a signal is output therefrom only when adescrambled signal is detected, whereby the content of the selected CATVchannel signal directly controls the operation of the decoder.
 2. Thedecoder of claim 1 further comprising means for determining whether CATVchannel signal is of the type to be descrambled by said descrambler. 3.A decoding system for coupling with a consumer electronic device toautomatically descramble scrambled video program signals, each of whichis transmitted on one of a plurality of radio frequency (RF) carrier andare received by said device; wherein said device includes means fordisplaying video program signals, a tuner for selecting one of saidplurality of RF signals, downconverting said selected RF signal to anintermediate frequency (IF) signal and forwarding said IF signal to saiddecoding system, wherein said IF signal consists of an IF carrier andsaid video program signal; and input port means for receiving adescrambled video program signal from said decoding system; the decodingsystem comprising: means for receiving said IF signal and downconvertingsaid IF signal to output said video program signal; means for analyzingsaid video program signal and determining whether said video programsignal is scrambled; means for automatically turning on or off means fordescrambling whether said video program signal is scrambled; means fordescrambling said video program signal if scrambled; and output portmeans for outputting a descrambled video program signal to said inputport means.
 4. The decoding system of claim 3 further comprising meansfor determining whether said video program signal is of the type to bedescrambled by said descrambling means.